Diode rectifier circuit



Feb. s, 1944. KE EF KE 2,341,325

DIODE'RECTIFIER'CIRCUITS Filed Aug. 29, 1942 I CONVERTER fujF/ERInventori Edwin W. Ken efake,

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Patented Feb. 8, 1944 DIODE RECTIFIER CIRCUIT Edwin W. Kenefake,Schenectady, N. Y., assignor to General Electric Company, a corporationof New York Application August 29, 1942, Serial No. 456,661

4 Claims.

My invention relates to diode rectifier circuits, and particularly tocircuits of this type adapted to detect signal modulations upon a highfrequency carrier wave and to supply the demodulated signal indicationsto the audio frequency amplification stage of an electric signalreceiver, such as a radio receiver, carrier current apparatus, or thelike.

The invention will be found to have particular application to balanceddiode detector circuits arranged to supply equal and opposite signalpotentials at audio frequency to the input of a pair of balanced orpush-pull audio frequency amplifying devices. It is well understood thatwhen a balanced or push-pull audio frequency signal indication isobtained from a single diode rectifier, the voltage to ground across thediode load is no more than one-half the maximum which may be obtained ifonly a single-ended audio amplifier were used. Where a negative biaspotential is to be obtained from the detector load for some controlpurpose such as automatic volume control or carrier-off noisesuppression, such a reduction of maximum voltage to ground isdisadvantageous.

Accordingly, it is an object of my invention to provide a new andimproved single diode balanced detection circuit particularly arrangedto facilitate the procurement of direct current bias potentials greaterthan those appearing across the diode load.

It is a further object of my invention to provide means forsubstantially insulating a single diode balanced detection circuit fromthe supply source in respect to unidirectional and signal frequencypotentials, thereby to facilitate efficient automatic volume control andcarrier-off noise suppression.

It is a specific object of my invention to provide a pair of singlediode rectifier circuits insulated from each other with respect tounidirectional potentials and arranged independently to supply abalanced audio input circuit and a maximum automatic volume control biaspotencarrier current appearing upon a conductor Ill. The signalmodulated high frequency oscillations appearing upon the conductor II]are supplied to a converter or mixer II where they are combined inaccordance with the heterodyning process with high frequencyoscillations of a different frequency from a local oscillator I2. Fromthe converter II a signal modulated Wave of resulting intermediatefrequency is supplied to an intermediate frequency amplifier I3, andfrom the amplifier I3 to an intermediate frequency output transformerI4. The primary and secondary windings of the intermediate frequencytransformer I4 are connected in parallel circuit relation with tuningcondensers I5 and I6 respectively.

Connected to the terminals of the secondary winding of the transformerI4, is a double diode rectifier I! having a pair of anodes I8, I9 and apair of heated cathodes 20, 2i. It will be understood of course that, ifdesired, a pair of single diode rectifying devices may be used in placeof the double diode IT. The diode rectifier comprising the anode I9 andthe cathode 2| is connected to provide a balanced or push-pulldemodulated signal voltage for supply to the control grids of a doubletriode push-pull audio am plifier 25 having a balanced output circuitcomprising an audio frequency transformer 26. The audio frequencytransformer 26 is energized from the plate circuits of the double triodeamplifier 25 and supplies from its secondary winding an amplified audiofrequency indication to a suitable signal reproducing device such as aloudspeaker 21. a pair of separate audio amplifiers may be used tosupply the balanced audio output transformer 26.

Since the diode detector circuit described briefly above utilizes only asingle pair of diode elements in the double diode rectifier H, the otherpair of elements comprising the cathode 20 and the anode I8 is madeavailable for obtaining a desired bias voltage for automatic volumecontrol and the like. For this purpose the rectifier I8, 20 may beconnected in series circuit relation with a load resistor 28 across thesecondary terminals of the transformer I4. The direct current biasvoltage then appearing across the resistor 28 will be the maximumavailable from the source I4 and will be proportional in value to thestrength of the incoming signal at the transformer I4. A suitableby-pass condenser 29 connected across the load resistor 28 shunts outundesired voltages of intermediate frequency and It will be understoodthat if desired insures that the load resistor 28 carries only directcurrent and audio frequency current. The secondary terminal 30 of thetransformer 16 is held at ground potential for intermediate frequenciesand higher frequencies so that no undesired voltage components of thesefrequencies appear in the automatic volume control lines 32 and 33.However, for unidirectional potentials and audio frequency potentialsthe point 3! is maintained at a potential below ground determined by thefull drop through the load resistor 23. This negative potential issupplied by means of leads 3|, 32, and 33 to suitable stages of thesignal channel ahead of the transformer M, such as the converter H andthe intermediate frequency amplifier 13. The negative bias suppliedthrough the Wires 32 and 33 controls the gain of the converter andamplifier stages in accordance with the strength of the incoming signalin such a manner as to tend to maintain substantially constant thesignal volume received at the intermediate frequency transformer 14.

For the purpose of permitting the demodulating circuit through the dioderectifier l9, 2! to operate at a lesser maximum negative unidirectionalpotential than the point 30 in the automatic volume control circuit, thediode l9, 2! is connected directly across the secondary terminals of thetransformer i4 through a pair of blocking condensers 35, 36, and thedetector load is connected in shunt circuit relation to the diode i9,2i. The condensers 35 and 33 are intermediate frequency condensers ofsuch small ca pacity that they offer substantially no impedance tocurrents of intermediate or higher frequencies but effectually insulatethe detector load circuit from the automatic volume control circuit andfrom the transformer terminal 30 for unidirectional and audio frequencypotentials. The balanced detection circuit itself comprises a pair ofserially connected load resistors 31, 33 having their common terminalgrounded and connected as a unit in parallel circuit relation with thediode rectifier 19, 2|. Interposed between the diode rectifier l9, 2iand the diode load 31, 3-8 is an intermediate frequency by-pass filtercomprising a pair of resistors 39, 40 and a capacitor ll. Since themidpoint of the resistors 31, 38 is grounded, instantaneous voltagesappearing across the resistors 31, 38 are equal in magnitude andopposite in polarity. This is the condition which is necessary forsupplying the input of a push-pull amplifier such as the double triodeamplifier 25, and for this purpose the opposite terminals of the diodeload 31, 38 are coupled through a pair of condensers 42, 43 to a pair ofserially connected audio input resistors M, 45. The midtap of theresistors 43, 45 is grounded through a squelch resistor 46 and aresistor 41. The resistor 41 is connected between ground and a source ofdirect current supply indicated by B+. The resistor 41 thus serves as apotent1- ometer to supply through the resistor 46 a certain amount ofpositive bias to the midtap of the input resistors 44, 45. The midpointof the resistors 44, 45 is also connected through the resistor 46 and asuitable grid bias resistor 33 to the common cathode 49 of the doubletriode aniplifier 25. Suitable taps on the audio input resistors 44, 45are connected respectively to the control grids E! and 5| of theamplifier 25.

To provide carrier-off noise suppression, a fsquelch tube 55 is arrangedto render inoperative the audio amplifier 25'upon the disappearance of acarrier wave at the transformer I l.

In the presence of a carrier wave the tube 55 is biased to cutoff by thenegative potential at the terminal 30 of the transformer I4 applied tothe control grid 56 of the tube 55 through a resistor 51. Upondisappearance of the carrier wave, however, the negative bias at thepoint 30 disappears, and the squelch tube 55 is permitted to passcurrent through a circuit which may be followed from a point of positivepotential upon the resistor 41 through the squelch resistor 46 and thetube 55 to ground. The current flowing through this circuit is in such adirection through the resistor 46 that it drives the grids 50 and 5| ofthe amplifier negative with respect to the cathode 49, thereby to cutoff both amplifying sections of the tube and render inoperative allsubsequent portions of the transmission channel.

From the foregoing detailed description of the 20 various elements of myelectric signal receiving apparatus and their manner of interconnection,it is believed that the mode of operation of the system as a whole willbe readily understood. By way of summary, however, it is desired topoint out certain features of the arrangement which are peculiar toapplicants invention. By arranging the diode detection circuits throughthe rectifier l9, 2| for balanced or push-pull audio indication with themidtap of the diode load resistors 31, 38 grounded, the bias potentialode IS, 20 in a series rectifying circuit including the load resistor 28for the procurement of a maximum negative bias potential for automaticvolume control and noise suppresion. Since full negative potential atthe transformer terminal 33 can be maintained only if this point isinsulated from the negative terminal of the balanced detector load, thebalanced load is shunt connected to the diode l9, 2| and insulated fordirect current from the transformer terminal 3!! by means of thecondenser 35. This arrangement permits the negative terminal of the biasresistor 28 to be operated at a different, and specifically a lower,direct current potential than the negative terminal of the balanceddiode load. Thus I attain at once with only the usual two dioderectifiers the advantages of a balanced or push-pull detector and amaximum negative bias for automatic volume control and the like.

While I have illustrated only one preferred embodiment of my inventionby way of illustration, many modifications will occur to those skilledin the art and it will therefore be understood that I intend by theappended claims to cover all such modifications as fall within the truespirit and scope of my invention. 7

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A receiver for electric oscillations comprising a source of signalmodulated carrier Waves, a first unidirectional conducting deviceconnected to said source, a first load resistor connected in shuntcircuit relation with said first. unidirectional conducting device, asecond unidirectional conducting device connected to said source inseresistor having an intermediate point of fixed potential thereby toproduce equal and opposite signal potentials at opposite terminal ofsaid first resistor, a push-pull load circuit connected across saidterminals, means for controlling the gain of said receiver in accordancewith the potential at a point on said second load resistor, and meansfor isolating said second load resistor from said load circuit inrespect to signal and unidirectional potentials.

2. An electric signal receiving apparatu comprising a source of signalmodulated carrier waves including a tuned circuit, a first dioderectifier connected to supply a negative bias potential proportional tothe strength of said signal to control said receiving apparatus, asecond diode rectifier and load resistor connected in parallel circuitrelation with each other and with said tuned circuit and having anoutput circuit connected in shunt with said load resistor to supplyequal and opposite potentials with respect to ground at signalfrequency, and means for substantially insulating both the anode andcathode of said second diode rectifier from said tuned circuit withrespect to unidirectional and signal frequency potentials therebyisolating said bias potential from said load resistor.

3. An electric signal receiving apparatus comprising a pair of dioderectifiers, a signal chan nel for supplying to said rectifiers a signalwave modulated at audio frequency in accordance with the desired signal,one of said rectifiers being connected with a first output circuit tosupply to said signal channel a negative bias potential proportional tothe strength of said signal, a second output circuit connected inparallel circuit relation with the other of said rectifiers and arrangedto supply equal and opposite potentials with respect to ground at audiofrequency, and capacitor means connected between said second dioderectifier and said signal channel thereby substantially to insulate saidsecond output cir cuit from said first output circuit with respect tounidirectional and audio frequency potentials.

4. An electric signal receiving apparatus comprising a signal channelincluding a tuned circuit for supplying a signal wav modulated at audiofrequency in accordance with a desired signal, a single diode rectifierconnected to said tuned circuit and having a shunt connected outputcircuit arranged to supply equal and opposite potentials withn'espect toground at audio frequency, a pair of electric discharge amplifyingdevices having a balanced output circuit, said balanced audio frequencypotentials being supplied to the input circuit of said amplifiers, asecond diode rectifier connected to said tuned circuit and to a loadresistor for supplying to said signal channel a negative bias potentialsubstantially equal to the strength of said signal, and a pair ofcapacitors interposed between said tuned circuit and said first dioderectifier thereby electrically to insulate said balanced load circuitfrom said negative bias potential.

EDWIN W. KENEFAKE.

